The author dedicated the work to the public domain by waiving all of his or her rights to the work worldwide under copyright law and all related or neighboring legal rights he or she had in the work, to the extent allowable by law.

SIR:
The Florida Geological Survey, through its cooperation with
other state agencies and with the universities of the Nation, is
able at moderate cost to have many excellent studies undertaken
and reports of the results of these prepared for publication by the
Survey.
These studies benefit the State by providing information on our
mineral resources and the author of the paper is provided funds
for a chosen research problem, the publication of which will make
him better known to his associates and may in some cases be used
as partial fulfillments of graduate degree requirements.
I am pleased to forward two papers herewith published as
Report of Investigations No. 9. One is entitled, "Dissolved Phos-
phorus in Florida Waters," and is written by Dr. Howard T. Odum,
Department of Biology, University of Florida. The other paper
was prepared by Dr. Alfred G. Fischer while attending Columbia
University, New York, and is entitled, "Petrology of Eocene Lime-
stones in and around the Citrus-Levy County Area, Florida." These
two papers compose the first of our "Miscellaneous studies."

Respectfully submitted,

HERMAN GUNTZR, Director

CONTENTS

PART I Dissolved Phosphorus in Florida Waters.

PART II Petrology of Eocene Limestones in the Citrus-
Levy County Area, Florida

43

Part I

DISSOLVED PHOSPHORUS IN FLORIDA WATERS

By
HOWARD T. ODUM

Department of Biology
College of Arts and Sciences
University of Florida

A basic survey has been made of the concentrations of dissolved
phosphorus in many types of Florida's surface waters. The ex-
tensive deposits of phosphate rock in Florida lead to unusually high
dissolved phosphorus contents in the streams and lakes which drain
these areas. Thus these waters are potentially of high fertility for
growth of aquatic organisms. Additional quantities of dissolved
phosphorus are being added by sewage and industry in some areas,
although little recognition has been made of the possibly large
biological effects that relatively small amounts of added phosphorus
can have on those areas which are not receiving drainage from
phosphate areas. The moderately low phosphorus content of basic
springs in contrast to acid surface streams suggests a controlling
role of pH in phosphorus solubility in Florida. It seems likely that
percolating rainwaters are continually concentrating phosphorus
in the layers just beneath the surface as the acid rainwater becomes
basic. The natural and artificial phosphates contributed to Florida's
surface streams hypothetically seem to be of the magnitude to con-
tribute to red tide phenomena and the rapid growth of water hya-
cinths in prescribed areas.

INTRODUCTION

Over the surface of the earth as a whole phosphorus is a scarce
substance and much in demand as it is an absolutely necessary
requirement for Man's civilization and indeed for all life. With-
out phosphorus no plants can grow and no food production is pos-
sible for Man or for fish and wildlife.
Phosphorus is a magic word in Florida because the extensive
natural phosphate rock deposits located near the surface have
directly and indirectly made many profound changes in the culture
of the State. Directly, benefits such as those developing from the
phosphate industry and from agricultural advances due to low
cost phosphate fertilizer have resulted. Indirectly, as the evidence
'The writer wishes to acknowledge the able assistance of Mr. Richard
Highton, Laboratory assistant.

2 FLORIDA GEOLOGICAL SURVEY

in this report suggests, sports fishing, commercial fishing, red
tide, water hyacinth growth, and pollution are all related to the
distribution of phosphorus dissolved in the Florida fresh and
marine waters.

Purpose and Scope of Investigation

The purpose of this study has been to analyze representative
samples of all kinds of Florida surface waters for dissolved phos-
phorus and to determine what relationships there are between:
dissolved phosphorus and the type of geological rock formations
underlying the area; between dissolved phosphorus and the type of
body of water; between dissolved phosphorus in Florida and in
other regions of the world; between dissolved phosphorus and the
processes of formation of phosphate rock; between dissolved phos-
phorus and the growth of aquatic organisms such as plants and
fish; between dissolved phosphorus and the increasing problem of
pollution of streams and estuaries; and between dissolved phos-
phorus and the spectacular red tide.

Cooperation and Acknowledgements
The data and interpretations have resulted from the cooperation
between the Department of Biology of the University of Florida in
Gainesville and the Florida Geological Survey with the aid of
many other persons. The Department of Biology furnished the in-
vestigator and laboratory facilities. The Florida Geological Survey
furnished the financial support for the assistant Mr. Richard
Highton and for supplies. The Office of Naval Research through its
support of another project on the productivity of Florida Springs
provided considerable aid indirectly since it was possible to collect
water samples in the course of this work. Mr. A. 0. Patterson,
District Engineer, Surface Water Branch, United States Geological
Survey, Ocala, Florida, furnished a large series of samples collected
by his staff throughout Florida. Mr. Ellis Landquist furnished a
series from Peace River. Series of marine samples were received
from Mr. William Beck, Florida State Board of Health; Mr. David
Karraker, University of Florida; Dr. Harold Humm, and Dr.
Nelson Marshall, Oceanographic Institute, Florida State University;
Mr. Forrest G. Wood, Marineland; Mr. William Jennings, Florida
Game and Fresh-water Fish Commission; Mr. K. Hansen, Univer-
sity of Florida, Dr. Minter Westfall, University of Florida, Dr. J.
B. Lackey, Department of Sanitary Engineering, University of

REPORT OF INVESTIGATIONS NO. 9

Florida; Mr. Kirk Strawn, University of Texas. The study was
much aided by discussions with the above especially as indicated in
the text. I am grateful to Dr. A. P. Black, Mr. R. Highton, Dr. J.
B. Lackey, and Dr. E. B. Phelps, University of Florida; Dr. G. A.
Riley, Bingham Oceanographic Institute, Yale University; and
Dr. R. O. Vernon, Florida Geological Survey for comment and
criticisms on the manuscript.

Previous Investigations
Over the world as a whole a very large number of studies have
established the geochemical behavior of the element and importance
of phosphorus to growth on land and in the lakes and ocean. Current
knowledge on this may be found in Hutchinson (1952) and Riley
(1951).
In Florida although much work has been done on phosphorus
in land deposits and its behavior in terrestrial agriculture, relative-
ly little knowledge has been accumulated about the phosphorus in
water. Routine analyses of waters have not included phosphorus
primarily because in contrast to the usual elements analyzed it is
present usually in small quantities, much less than a part per
million. However, it is this low concentration that makes the
element important. Along with dissolved nitrogen dissolved phos-
phorus has been shown to be the usual limiting factor to growth
in waters in, other regions.

Specht (1950) has published a series of analyses of phosphorus
dissolved in fresh water of Peace River in a report on phosphorus
pollution. Additional analyses of this river have been made by
Florida State Board of Health but have not been published.
Some data on the estuarine and marine waters from the Miami
area have been published by Miller (1952) and from waters as-
sociated with the red tide phenomenon by Ketchum and Keen
(1948).

A general survey of the phosphorus over the whole State has
been needed in order that the values in special situations could have
comparative meaning. The results and principles of general sur-
veys of this sort which have been done in Wisconsin by Juday,
Birge, Kemmerer and Robinson (1928) and in marine waters by
Redfield, Smith and Ketchum (1937) can not be directly applied
to Florida because the State has extensive rock phosphate deposits

FLORIDA GEOLOGICAL SURVEY

and Wisconsin does not. In turn the study of phosphorus behavior
in an area where phosphorus minerals occur abundantly can con-
tribute to the general understanding of this critical chemical ele-
ment the world over.

Methods
Samples were collected in 100 to 400 cc. soft glass bottles with
vinylite lined plastic caps. About two-thirds of the samples col-
lected received several drops of chloroform in order to reduce the
fixation by adsorption and bacteria of the dissolved phosphorus on
the walls of the bottles. Where the quantity of phosphorus present
is in concentrations of the magnitude of .020 ppm., the loss to bottle
walls has been shown to be appreciable (Harvey, 1948). Phos-
phorus is present in waters as fine particulate matter, as dissolved
organic compounds, and as dissolved inorganic phosphate. Except
in a few cases no attempt was made to distinguish between these
fractions because the partition of phosphorus changes rapidly
due to the action of organisms in the sample bottles. Thus with
the delay inherent in the sampling, it was only feasible to make
determinations of total phosphorus in most cases. The total phos-
phorus is of primary interest because in the course of one day the
phosphorus in a natural body of water may fluctuate between an
inorganic fraction and an organic fraction during phytoplankton
plant photosynthesis and decay.

Samples of 100 cubic centimeters were digested with acids over
a hot plate to convert all fractions into inorganic phosphorus, a pro-
cedure used by Robinson and Kemmerer (1930). When this solu-
tion was diluted to 50 cubic centimeters, a blue color developed pro-
portional to the phosphorus content. The intensity of color after
five minutes was measured in a Klett Summerson colorimeter. A
graph was prepared of the color intensity of known standards that
had been treated in the same way as the samples. The concentration
of phosphorus in unknown samples was obtained from this graph.
With homogeneous materials this method has been reported with
an accuracy of reproducibility of 5-10%. For a single series the
data in Table 1 and the data for Silver Springs (Table 2) indicate
a similar accuracy in these analyses. However for heterogeneous
materials and for the lower concentrations it is likely that the
errors are considerably greater. Fortunately the types of differ-
ences discussed below seem to be much greater than can be ac-
counted for as experimental error by the largest estimate.

In waters that are highly saline the blue color has been shown
to be depressed by some interaction with the salts (Robinson and
Thomson 1948). This error is usually compensated by analyzing
standards to which low phosphorus sea water has been added and
deducing a correction usually between 1.1 to 1.35. In this survey
a correction of 1.2 was used for saline waters. However for these
very varied waters of contrasting qualitative salt compositions and
varying salinities, considerable error has necessarily been incorp-
orated by such a procedure. Thus the error is possibly 20%
greater for saline than for fresh waters. The analyses include
any small quantities of arsenic which may act with phosphorus in
this test.

REPORT OF INVESTIGATIONS NO. 9

PATTERNS OF DISTRIBUTION OF DISSOLVED PHOSPHORUS

Dissolved Phosphorus and Geological Formations

In general most of the dissolved contents of waters are derived
from the rocks over which the waters flow. Thus it is a reasonable
hypothesis to expect the dissolved phosphorus in waters to cor-
respond to the type of underlying rock.
The phosphate bearing formations in Florida are primarily
the Miocene Hawthorn formation, Alachua formation, and Duplin
marl and the Pliocene Bone Valley formation. The areas of out-
crops of these rocks in Florida are shown in figure 1.

The streams that cross these formations and the total phos-
phorus content of their waters in parts per million are shown in
figures 2, 3, 5, 7 and 9. In much of Florida a close correlation
exists between the phosphate areas and the dissolved phosphorus in

/ Union Co.

Block
Creek

Co.
(5a,

Clay Co.

013

A-/

-Lake Santo Fe

SIm
S Alacho CGo.
MILES
0 0 '....

( Hawthorn

Levy Co.

formation

V Duplin marl

Putnam Co.

Oklowaha R.

IMarion Go.

i

r a.141
Orange Lake

7<43

Figure 2.-Dissolved phosphorus in the region of Gainesville, Florida,
and the phosphatic Hawthorn formation. (Position of formations after
Cooke, 1945)

d

FLORIDA GEOLOGICAL SURVEY

the waters. The correlation seems good in the north central Florida
area and in the Bone Valley phosphate mining district in central
Florida. Some relatively high values that are not associated with
phosphatic geological formations are due to pollution. Some de-
posits are not crossed by major streams and therefore correlative
data are lacking on these. The analyses for Alachua County, figure
2, show the manner in which the dissolved phosphate reflects the
geology. In figure 3, lines of equal phosphate concentration have
been drawn over the whole State much as one would draw lines
of equal height on a topographical map. These are of course ap-
proximations but serve to emphasize the superposition of areas
of high dissolved phosphate concentration over known phosphate
deposits.

talline rock areas possess slightly lower dissolved phosphate con-
tents than the central lowland sedimentary area. These results con-
firm in a striking way the general principle of the geologic control
of phosphate content of the waters, and it is possible that future
prospecting may be facilitated by analyses of dissolved phosphates
in stream systems.2 It has long been known that dissolved phosphor-
us is so scarce in the ocean that it is rapidly removed by phytoplank-
ton and lost to the deeper water through sedimentation of organic
detritus so that the upper ocean waters are maintained in an im-
poverished condition receiving a little phosphorus for growth only
from turbulent exchange of the element brought up from the deeper
waters and in from rivers (Riley, 1951). The analyses of estuarine
waters of Florida further document this pattern by showing that
Charlotte Harbor and Tampa Bay are one of the richest phosphatic
areas and receive more dissolved phosphate from streams than any
other estuary in Florida.

Dissolved Phosphorus and the Type of Water

The essential features of the distribution and circulation of
phosphorus within streams, lakes, ground waters, and estuaries
have. been established in other regions (Juday, Birge, Kemmerer,
and Robinson 1928; Mortimer 1941-1942; Hutchinson 1941; New-
combe 1940). In general, streams and ground waters have been
2It is amusing to remember the excitement that arose in the laboratory
when waters from the Econlochatchee River were found to possess relatively
enormous phosphorus concentrations although no phosphate districts were in
the drainage. It was learned that a recent shift in the disposition of the
Orlando sewage into this river accounted for these values.

Figure 5.-Dissolved phosphorus in the Peace River
system. Data obtained in cooperation with Mr. Ellis
Landquist.

REPORT OF INVESTIGATIONS No. 9

found to contain moderate amounts of dissolved phosphorus derived
from the rock strata in an inorganic form. In streams with little
or no plankton and attached plants the volume of water is large
compared to the number of plants that derive phosphorus for
growth and thus there is more phosphorus than is needed in plant
metabolism. But the situation shifts when these waters flow into
lakes where the relatively still waters in the upper levels support
microscopic floating plants which take up the phosphorus and con-
vert it into the phosphorus of organic matter. Then the lack of
phosphorus often becomes limiting to plant growth. When these
tiny single celled plants are eaten by microscopic plankton animals,
the phosphorus may be transferred into other organisms and
eventually returned to the water as dissolved organic phosphorus or
deposited on the bottom as particulate phosphorus. Thus the in-
organic phosphorus in shallow lakes and in the upper levels of
deeper lakes is small and the organic phosphorus is only a little
more. But in the bottom waters of the deeper lakes much larger
concentrations of phosphorus are found during the summer strati-
fication. Here the chemically reduced conditions associated with
lower oxidation reduction potential and sometimes lower pH and
the absence of green plants cause more phosphorus to remain in
solution both as dissolved inorganic phosphorus and dissolved
organic phosphorus. Thus the processes within the lake remove
phosphorus from water as it flows through the lake and deposit it
in the lake's lower waters and sediments. It has been shown thus

Figure 7.-Dissolved phosphorus in the Tampa Bay region, Florida. Data
obtained in cooperation with Dr. Nelson Marshall, Florida State University in
the fall, 1952.

that lakes are a phosphorus filter as in River Sussa, Denmark (Berg,
1945). In a similar manner, when phosphorus laden river waters
reach the sea the phosphorus is removed and deposited on the bot-
tom of the ocean in the sediments. Estuarine waters are zones of
mixing where the phosphorus content is intermediate between
rivers and sea.

With the above introductory account of the occurrence and
distribution of phosphorus in natural waters, it is interesting to
compare data from Florida as summarized in tables 2, 3, 5, 6, 7. It

12

REPORT OF INVESTIGATIONS No. 9

will be noticed that streams are high and in fact enormously laden
with phosphorus in the phosphate districts. The lake waters at
the surface have smaller amounts than the streams because of the
filtering action of the lakes. Estuarine waters contain more phos-
phorus than open, water, as reported in the literature, but somewhat
less than the.streams from which the phosphate is derived. In com-
parison to lakes, streams and estuaries which receive high values
in phosphate areas, the spring waters have moderate values irre-
spective of the area in which they occur. As shown in the Silver
Springs analyses the springs have primarily inorganic phosphate,
the organic phosphorus having been removed by the soils and rocks
of the recharge areas. The spring waters in these limestone areas
are basic so that little calcium phosphate is dissolved and very
little can be held in solution. Thus pH is critical in regulating the
amounts of dissolved phosphate of inorganic form but not that of
the organic phosphorus. The solubility of calcium phosphate under
a variable pH is represented in Table 4. However, calcium phos-
phate is found in nature usually in some type of apatite mineral,
a complex chemical composition, upon which no such solubility
tables are available.

TABLE 3
MEAN VALUES OF PHOSPHORUS IN TYPES OF FLORIDA WATERS
Water Types / ppm Total P
Phosphate District Other
Streams .876 (18) ----.046 (44)
Estuaries .269 (2) .._.044 (21)
Lakes .290 (8) .038 (31)
Springs .061 (5) _045 (27)
(The number of different bodies of water average in each case is indicated by
the figure in parentheses).

Figure 8.-Dissolved phosphorus in the rivers and canals of south Florida
during August 1952.

Among the lakes there are great ranges of phosphate contents
just as there are great ranges of conditions such as hardness, car-
bon dioxide and color. The vertical pattern of phosphorus distri-
bution within Lake Mize, Florida, is similar to that of Lake Mary,
Wisconsin, although the values are much higher for these two lakes
than for most of the other lakes reported in Wisconsin or elsewhere

REPORT OF INVESTIGATIONS No. 9

(see figure 4 and Juday and Birge, 1931). These lakes are similar
in being deep soft seepage lakes with high phosphates possibly due
to low pH. Lake Mary, Wisconsin, is very atypical. It is not known
whether the stratification of phosphorus in Lake Mize is typical for
Florida's relatively few deep lakes.

The data in Table 6 indicate that some of the lowest values are
found in waters where attached littoral plants have possibly had
a r61e in depleting the waters such as in marshy pools surrounding
lakes, pools along roads, and small lakes without appreciable drain-
age in the sandhills. The action of a lake in filtering phosphorus
is illustrated in figure 2.
Data from analyses of water entering Orange Lake from the
north and discharging eastward into the Oklawaha River show
a marked decrease in phosphorus content. Also in figure 2, the
waters entering Newnans Lake, the moderate sized lake just east
of Gainesville, show a drop from a phosphorus content of .247 to
.117 ppm.

FLORIDA GEOLOGICAL SURVEY

locksonville

lower St.Johns

sources

Atlantic Ocean

.086

seWOa

Econ

0 10 20 3
MILES

upper St. Johns R

Figure 9.-Dissolved phosphorus in the St. Johns River system.

ppm P

V

REPORT OF INVESTIGATIONS NO. 9

The general impression that one obtains, that water filled sinks
are often fertile, is supported by the analyses of phosphorus. Ap-
parently the water filling the basins are phosphorus laden in con-
trast to the deeper artesian aquifers as represented by the large
springs which have moderate phosphate values.

The classification of analyses according to the type of water as
given in Table 6 suggests some relationship between the percentage
.of dissolved phosphate and the type of lake water but a general
classification of the water types biologically is one outstanding
problem not yet completed. In Table 6, it should be noted that the
high phosphate contents are found in small acid streams which had
relatively short surface courses since falling as rain. The more
basic waters which have received ground waters and salts have
lower values depending of course on the rocks through which the
water passed.
Ohle (1934) found higher values in German dystrophic waters
(brown waters) than in clear waters. Similar results noted in
Florida are suggested as due to the soft acid nature and to the
course of these waters. Also Barbier and Maroger (1950) have
shown that colloidal humates increase the amount of calcium phos-
phate that is dissolved by binding action. Humates are brown mo-

Standing Waters:

FLORIDA GEOLOGICAL SURVEY

lecular and colloidal breakdown products of the lignin that in natur-
al wood holds the fibers together and in Florida stain many streams
brown.

Dissolved Phosphorus in Florida Compared with Other Regions

Since Florida has such large resources of phosphate rock, it is
reasonable to expect Florida's waters to contain on the average
higher phosphorus concentrations than most other regions of the
world. G. E. Hutchinson, in an unpublished manuscript, collected
data on dissolved phosphorus in lakes to which averages of Florida
data have been added and both are presented as Table 5. This table
indicates that Florida has higher dissolved phosphorus concentra-
tions than the rest of the world with humid climate, with the pos-
sible exception of those districts elsewhere that indicate major
phosphate deposits. Of those analyzed only the salt lakes in arid
parts of the world show higher phosphate contents than those of
the phosphate districts of Florida. It is interesting that the areas
that are most similar to Florida are the sedimentary North Ger-
many area, which resembles Florida in some respects such as
elevation and general geological structure, and the Gran Chaco
of Paraguay, which has a somewhat similar climate. In contrast,
waters in crystalline rock areas are low and the older and more
modified sedimentary areas are intermediate in dissolved phos-
phorus concentrations such as shown for Connecticut and Sweden
in Table 5. It is likely that other areas of the world possessing
phosphate districts, such as North Africa, Idaho, Esthonia, Egypt,
etc., (Johnson, 1952), would similarly possess high dissolved
phosphorus.

Dissolved Phosphorus and the Origin of Phosphate Deposits
No wholly satisfactory explanation has become accepted for
the origin of Florida's extensive and varied phosphate deposits.
The status of knowledge on this is discussed in detail by Vernon
(1943, 1951). Apparently a combination of initial deposition of
phosphatic minerals, bones and teeth in marine and terrestrial
sediments followed by a possible later concentration of these parts
of the sediments have produced the existing deposits. Although
there is little evidence of phosphate deposition during the Recent,
other than at bird and mammal rookeries, following the hypothesis
of uniformitarianism we look at contemporary Florida for answer
to the processes in past geologic time for there is little evidence

REPORT OF INVESTIGATIONS NO. 9

that Florida is geologically much different now than it was in the
Tertiary times.
An examination of the data on dissolved phosphate from the
present Florida waters suggests two things: First, the marine
estuarine deposits now forming off some rivers are forming in the
presence of relatively high phosphate concentrations so that these
sediments may be expected to contain a proportionately high phos-
phate content. Miller (1952) has shown for Biscayne Bay in the
Miami area that the ratio maintained between dissolved phosphorus
and the sedimentary phosphorus is about 1/1000. The high phos-
phorus contents of the rivers moving into sea water are possibly
supersaturated in relation to the high calcium, basic, ocean waters
as estimated theoretically by Dietz, Emery, and Shepard (1942).
Second, the highest dissolved phosphorus contents have been found
where soft acid streams crossed phosphatic formations suggesting
that acidity regulates the amount of phosphorus which becomes
dissolved.
Since the basic spring waters are moderately low in dissolved
phosphorus, even in phosphatic districts, it seems that phosphorus
may become dissolved in the surface drainage water but becomes re-
moved again as the ground water passes through deeper strata.
This suggests a mechanism by which the deposits already rich in
phosphorus now found most abundantly a few feet below the sur-
face have been enriched. First the phosphorus is dissolved and then
redeposited'as the water becomes more basic on reaching the deeper
ground water levels and as the initial carbon dioxide acidity is
neutralized with the limestone. Those acid surface waters moving
down surface streams to the sea gradually become basic but much
of the dissolved phosphorus by this time is converted into the
organic phosphorus of plant and animal matter in particulate,
colloidal, and dissolved form so that it remains in solution in estu-
arine waters for some time in spite of high pH. Thus the difference
observed between the high phosphorus content of acid surface
water and the low phosphorus content of more basic ground waters
indicate that phosphorus leached out of one layer can be precipitated
in the rocks through which it may pass or that the ground water was
relatively free of phosphorus at the recharge area.
That enrichment of phosphorus may occur in existing forma-
tions due to the above causes does not imply that the present phos-
phatic formations are themselves older formations concentiate'd by
leaching. The Alachua formation of Florida (Vernon, 1951) is

19

FLORIDA GEOLOGICAL SURVEY

typical of those phosphate deposits formed by the fixation of phos-
phatic acid solutions through reaction with carbonate rocks. Ver-
non (1951) using detailed stratigraphic data from Citrus and
Levy counties, Florida, found that Miocene phosphatic formations
(Hawthorn and Duplin marl) were probably laid down in shallow
seas adjacent to a land mass upon which the phosphate of the
Alachua formation was forming. He feels that the high phosphate
content of these formations was derived from a high dissolved
phosphate level in the sea and adjacent land at the time of for-
mation.
The solubilities of calcium phosphate in fresh water of varying
acidity shown in Table 4, have been modified from Green and
Holmes (1947). These solubilities are based on the theoretical
equation for the solution of excess tricalcium phosphate under
equilibrium conditions, and in the ionic strength of fresh water.
Although these assumptions rarely correspond exactly to natural
conditions, the important role of pH and calcium concentration is
demonstrated nevertheless. Acid soft water streams have capacity
for taking up very large concentrations of phosphorus mineral
matter through which they pass whereas basic hard waters such
as in Florida's ground waters, even at equilibrium can hold less
than one part per million. The values for the large typical Florida
Springs of .020-.123 ppm P with pH ranges mostly between 7.3
and 8.3 with calcium concentrations 30 to 70 ppm are only slightly
above those predicted by Table 4.

For salt waters the assumption used in calculating these data
do not apply, for solubilities of many substances in saline waters
are greater due to the greater ionic strength. The greater ionic
strength in part counteracts the effects of high calcium in sea
water. However, from similar calculations based on greater ionic
strength Dietz, Emery, and Shepard (1942) found that the ocean
is possibly saturated with phosphorus. The unusually high phos-
phorus values reported in Tampa Bay and Charlotte Harbor are
of course total values including organic and colloidal fractions.
Note that if some source of acidity such as industrial pollution
should lower the pH much greater phosphate solubilities are
possible and although later neutralized this mechanism would
permit the introduction of high phosphate concentrations into or-
ganic fractions and into colloidal and soluble form. Bear Branch,
which receives wastes from a superphosphate plant near the town
of Bartow, was reported by Mr. Ellis Landquist in his biological

20

REPORT OF INVESTIGATIONS No. 9

study of the Peace River during 1950-51 to possess a pH range from
2.5 to 6. Such acidity accounts for the dissolved phosphate contents
up to 177 ppm phosphorus in this branch. Although subsequently
diluted by the Peace Creek, the high values of 5 ppm which per-
sisted in the Peace Creek below this point (see figure 5) seem to
have been due to this pollution since other streams in the system
at the same time had dissolved phosphorus values ranging .5 to
3 ppm.
Some observations made of the dissolved phosphorus in streams
in the Devils Millhopper, a large sink near Gainesville, may be
interpreted as in agreement with the hypothesis of concentration
discussed above. Several small springs issue from the sides of
the Millhopper and one stream falls into this sink from the surface.
These flows rush down the sides and out through a fissure in the
bottom of this 80-foot hole. The sink penetrates the Hawthorn
formation which is heavily phosphatic. The data presented as
figure 6 indicate that the water which has passed through the
ground has a lower phosphate content than the water that flows
in over the top of the sink. If surface water does lose its
phosphorus upon passing through rock, there should be a concen-
tration of phosphate not far below the soil surface in areas of
ground water recharge. Such a concentration has not been de-
termined, but may be present.

Dissolved Phosphorus and Potential Fertility
As indicated in the introduction, all life requires phosphorus
as a basic chemical material for its metabolic processes. About two-
tenths of one per cent of phosphorus is required to make chromo-
somes in the cells and to make coenzymes and other energy trans-
forming substances. In most aquatic environments it has been
substantiated by many workers (Hutchinson, 1952) that the growth
of plants, and the subsequent growth of animals that derive nu-
trition from these plants, is limited by the amounts of phosphorus
and nitrogen available and utilized by the plant. In fresh waters
of many tropical areas blue-green algae are abundant and fix nitro-
gen from the air to help supply the nitrogen requirements, and
thus cause phosphorus to be the limiting factor in plant growth.
Hutchinson (1937), in discussing lakes in desert regions considered
values of phosphorus over .050 as certainly not limiting. There is
some evidence that this is true in Florida, for continual blooms of
blue-green algae through the long summer have been reported to

21

FLORIDA GEOLOGICAL SURVEY

me in personal communication by J. C. Dickinson and in the
monograph on the St. Johns River by E. L. Pierce (1947). There
are of course many other factors affecting the biological produc-
tivity of waters and where phosphorus and nitrogen are not so
scarce as to limit growth, these other factors will determine the
production of protoplasm by the natural community of organisms.
For example, trace elements such as copper and cobalt may be
limiting.
The phosphorus distribution is not expected to be the same as
the distribution of high production but the dissolved phosphorus
can be thought of as a measure of potential productivity and fer-
tility. The phrase potential fertility is used in the sense of phos-
phorus availability. Other things being equal regions of high
phosphorus might be proposed as regions of high fertility. This
is very important to Florida. The growths of microscopic plants
that support fish and other fauna are fundamental to the pros-
perity of commercial and sports fishing, both of which are very im-
portant to Florida's tourist trade. Someone with experience in
other regions quickly gains the impression that the waters of the
State are fertile and contain much life. Indeed, with a very high
annual sunshine average and with its waters carrying considerable
phosphorus, one suspects that productivities may be high on a
world basis. There are little data as yet to test such a hypothesis,
but it can be said that the potential fertility of the State, as meas-
ured by the dissolved phosphorus, is very large.
Although a high fertility is generally a good thing from man's
point of view in that more life is produced in the lakes, streams and
estuarine waters, it is not necessarily so. If the fertility results in
the proliferation of some objectionable organism or does not pro-
duce the desired type of organism, then either less fertility is
needed or some control needs to be exercised over the type of
organisms which are permitted to make use of the potential fer-
tility. The clogging of waters by water hyacinths is an example
of an undesirable result of high fertility. Another is the over-
production of undesirable fish species in some waters at the ex-
pense of species desired for food or sport.
Superficially the distribution of high potential fertility as meas-
ured by high concentrations of dissolved phosphorus in figure 3
suggests a possible relationship to the areas of water hyacinth
nuisance. Certainly, rapid growths of these plants occur in the St.
Johns, Peace and Suwannee river systems and in the lakes of the

22

REPORT OF INVESTIGATIONS No. 9

phosphate district such as Newnan Lake and Orange Lake in
Alachua County. Indeed, this possible correlation should be in-
vestigated and comparative growth of hyacinths measured in dif-
ferent waters.
Much work has been done in ponds of other areas to increase
the fertility of water by artificial fertilization similar to that done
in terrestrial agriculture. However, nothing has been done to work
out a method for decreasing the potential fertility of a water
should it be deemed advisable. Actually this is a major engineering
need since great sums of money are spent each year killing algae
blooms in lakes in which clear water is desired rather than rapid
production. The approach to the problem of using chemicals is
rather a backwards approach for whenever blooms of algae or rafts
of hyacinths are killed, the phosphorus within them is released
into the water and into the lake muds so that the remaining or-
ganisms grow even faster. A much better approach would be one
designed to remove the phosphorus. Commercially this might be
possible since the dissolved quantities involved are so small, being
usually much less than one part per million. As yet, no practical
solution seems to be at hand. Perhaps a biological filter is feasible
in which phosphorus and plant growth are removed from water
running through a lake, with resultant improvement downstream,
or perhaps ferrous or aluminum salts could be added to remove
the phosphorus as a precipitate.
An understanding of the quality and quantity of the aquatic
production under various situations in Florida is needed. A con-
certed research program should be made to uncover the basic fac-
tors and their interactions, which control this natural aquatic agri-
culture.
It is likely that phosphorus fertilization of the Florida waters
which contain more than .050 ppm total phosphorus will not in-
crease biological production because it is probably not limiting at
these concentrations.

Dissolved Phosphorus and Pollution

Some types of pollution produce extreme effects on the potential
fertility of Florida's waters by adding large amounts of dissolved
phosphorus relative to the amounts naturally present. By pollution
is here meant the addition of materials to a natural body of water
as a result of man's activity so that the conditions of the lake,

23

FLORIDA GEOLOGICAL SURVEY

stream, or estuary are markedly changed with respect to the
quality and quantity of biological growth. By this definition a pol-
lution may not necessarily be bad if the man made changes are not
undesirable to the long range welfare of all concerned. However,
pollution by changing the natural situation often restricts the
variety of organisms and often markedly affects the populations
of fish organisms in indirect ways by affecting their plant and
animal foods.
In Florida two sources are at present increasing the dissolved
phosphorus in Florida waters: Industrial and municipal sewage
and the byproducts of the phosphate industry. Phelps and Barry
(1950) have summarized sources of pollution in Florida. When
sewage is passed through chemical treatment many of its ob-
jectionable properties, such as disease organisms and organic
matter, are removed, which if dumped directly in streams would
use up tht dissolved oxygen and kill the organisms. However, the
very high content of phosphorus in urine and in the solid materials
of raw sewage is not completely removed by sewage treatment
plants. By the time the decomposing raw sewage reaches the plant
there is already a high concentration of phosphorus in the dissolved
inorganic form. Apparently this inorganic fraction passes through
the plant without much loss. Raw sewage entering the university
sewage plant in Gainesville, April 9, 1953, possessed a dissolved
inorganic phosphorus content of 2.1 ppm. The final effluent emerg-
ing from the same plant contained 1.9 ppm dissolved inorganic
phosphorus. These values in comparison to the natural concentra-
tions in most streams are enormous.

A sample of the phosphorus developed from Lakeland sewage
and taken out of Lake Hancock in Saddle Creek and analyzed was
2.0 ppm. and a sample of the Orlando sewage taken in the Econ-
lochhatchee Creek analyzed 3.2 ppm. Standard engineering prac-
tice has not recognized these relatively small phosphorus quantities
on a weight basis as being a pollution. Considering the possible
stimulus to undesirable growths or undesirable species, it is clear
that this may at times be harmful although a general increase in
fertility is promoted in some fish culture. With the increasing popu-
lation of Florida and the increased dumping of sewage into
Florida's i relatively small surface streams, the result of this practice
must be studied. It is certainly not possible to say from the avail-
able evidence whether the character of Florida's freih waters and
estuaries, which are an important resource, are being markedly

24

t-x

REPORT OF INVESTIGATIONS NO. 9 25

changed and if so whether for the better or worse by these large
changes in potential fertility. It is, however, important that the
total biological character of the major water types be established
before and after such increase in potential fertility to determine if
there is a resultant increased hyacinth growth, game fish, or algae
blooms in previously clear waters.

The phosphate industry particularly in the Peace and Alafia
river systems is discharging phosphate slimes and, in the case of
Bear Branch, Bartow, Florida, acid waters high in dissolved phos-
phorus into a river which must already have had high concentra-
tions because of the underlying rock formations. A high original
phosphorus concentration is indicated by the streams in the Peace
and Alafia river area which do not receive industrial wastes but
have very high values although not as great as the Peace and Alafia
proper. It seems likely that the pollution somewhat accentuates
the addition of phosphorus. The data in figure 5 support this.
Relatively undisturbed Charlie Creek, for example, has a lower
phosphorus value than the streams receiving wastes. It is unlikely
that at these high levels phosphorus is limiting in the Peace River
or that the potential fertility is in any way realized. But the effect
on the fertility of Tampa Bay and Charlotte Harbor is probably be-
ing increased by the increase in phosphorus going down these rivers.
Phosphorus also goes down the Peace River through Lake Hancock
from Lakeland sewage. The problem of the possible effects of
colloidal and slime phosphorus on river organisms is a separate
problem that is being studied by Mr. Ellis Landquist of the Uni-
versity of Florida.

Dissolved Phosphorus and the Red Tide

If there are increasing quantities of phosphate going down
some rivers, the question is raised whether this additional fertility
is increasing the incidence of the red tide offshore. The so called
red tide is a bloom of a microorganism Gymnodinium brevis in
marine waters which becomes so concentrated that fish are killed in
large numbers and are washed up in great quantities on the beaches
(Gunter et al, 1948).

Much work has been done to show that similar phenomena
occur in many parts of the world at widely timed intervals.
Walton Smith (1949) postulated that the occurrence is due to nu-
trients becoming available, especially phosphorus. Ketchum and

FLORIDA GEOLOGICAL SURVEY

Keen (1948) found unaccountably high total phosphorus concentra-
tions in the 1947 growth off the coast at Sarasota. As yet, however,
there is no definite proof that high phosphorus concentrations are
required for red tide blooms.
Slobodkin (1952) has postulated that the relatively frequent
red tide occurrence off the lower Florida west coast is a result of
rains and northeast winds which carry low salinity waters con-
taining a few of the Gymnodinium organisms and nutrients out over
the saltier open waters where they develop a bloom and then drift
northward and shoreward in the prevailing Gulf drift. The mechan-
ism of this drift was demonstrated by E. L. Pierce (1951). Specht
(1950) has shown high phosphorus concentrations entering Char-
lotte Harbor from the Peace River. From the data in figures 3 and
7 it is suggested that the Peace and Alafia rivers are sources, of
larger nutrient concentrations than the Caloosahatchee and Okee-
chobee which have smaller amounts of dissolved phosphorus. The
Caloosahatchee river crosses phosphatic formations but is derived
largely from phosphorus poor Lake Okeechobee and is not so acid
when it crosses phosphorus rocks. A charge of phosphate laden
low salinity water might accumulate in Tampa Bay or Charlotte
Harbor and then be blown out to sea as a fairly intact mass of
water before mixing.
The data in Table 7 suggest that adequate phosphorus is found
in these waters in excess of that needed for a red tide bloom. After
the initial bloom further fertilization can come from fish that swim

into the area, die and decompose. The data on samples collected
from the recent red tide in 1952 by N. Marshall show that lower
concentrations are required at least in these last stages of the bloom
than might have been surmised from the values taken by Ketchum
and Keen (1948). Perhaps, however, during the last stages, the
bloom was being dispersed by mixing although the water was
recognizably red at the time. To further test these hypotheses a
continuous series of samples must be taken regularly until the initial
formation stages of the red tide are covered. Of course adequate
phosphorus does not guarantee a bloom for there are other factors,
but certainly adequate phosphorus is a prerequisite (Specht, 1950;
Smith, 1949; Ketchum and Keen 1948) .

If the phosphate going down the rivers into the coastal areas
in large amounts is increasing due to expansion of industry and
population, further examinations must be made to determine
whether the general fertility of some coastal waters is being in-
creased and whether or not this is following desirable lines or
is producing undesirable products. The procurement of adequate
fishing statistics may permit some examination of change in this
respect.

3(This note was added in press.) Three recent papers and a fresh outburst
of red tide in September 1953 at the mouths of Tampa Bay and Charlotte Har-
bor have further increased interest in red tide phenomena. (Kierstead, H.
and L. Slobodkin, 1953. Journ. of Marine Research, vol. 12, pp. 141-147; Slo-
bodkin, L., 1953. Journ. of Marine Research, vol. 12, pp. 148-155; Chew, F.,
1953. Bull. of Marine Science of the Gulf and Caribbean, vol. 2, pp. 610-625.)
Slobodkin proposes that a lens of brackish water blowing out from shore on
the surface provides a means of developing a critical minimum mass for
starting a full bloom. He thinks that the nutrient phosphorus could be con-
centrated by organisms migrating vertically into the surface layer. Thus he
thinks that the amount of phosphorus initially present need not be larger
than usual. Chew found patches of low salinity water offshore but found
that the red tide was not in these but was in slightly higher salinity waters
nearby. He interpreted the lower salinity water as derived from rivers and
the higher salinity water which was high in phosphorus as derived from
offshore. It seems possible that Chew's lower salinity water could have been
from the Caloosahatchee and the red tide water could have originated further
north in the polluted Tampa Bay estuary and Charlotte Harbor. Slobodkin's
idea of critical mass seems more applicable if applied to nutrient containing
water from the polluted estuaries. Even if phosphorus is not a limiting
nutrient to red-tide blooms, it is likely to be correlated with limiting nutrients
from the polluted bays and thus act as a water marker in tracing such
water. The repeated localization of the red tide blooms in areas near the
mouths of the phosphatic rivers suggests that some causal factor is localized
there.

27

FLORIDA GEOLOGICAL SURVEY

CONCLUSIONS
1. The dissolved phosphorus content of Florida fresh waters is
correlated with the underlying phosphatic rock formations of the
drainage area.
2. The dissolved phosphorus content of Florida estuarine waters
is determined by the proximity of the rivers and the phosphorus
content of these rivers.
3. In the phosphatic districts the dissolved phosphorus is highest
in the soft acid streams, lower in lakes due to a biological filtering'
action, and lowest in springs possibly due to a geological precipitat-
ing action.
4. The dissolved phosphorus and thus the potential fertility in
Florida waters especially in the phosphatic districts is considerably
higher than in waters in most other humid regions of the world
yet studied.
5. Dissolved phosphorus liberated by sewage and by the phosphate
industry is producing a high potential fertility in many waters.
There is no definite evidence whether or not this is desirable.
6. The high frequency of the red tide off the mouths of the Peace
and Alafia rivers suggests causal relationship between the large
quantities of natural and industrial phosphorus passing down these
rivers.
7. A program of research is needed to discover what other factors
determine how the high potential fertility of Florida's waters is
expressed in terms of fish production, water hyacinth growth, and
cloudy waters. The natural condition of Florida streams should
be studied and recorded as a valid basis for resource use manage-
ment before further pollution destroys our chance to establish the
biological structure of the natural streams.

Alfrei by
MH George Fischer
THE NATURE OF THE PROBLEM
The Eocene sediments of the Florida peninsula consist of
relatively pure carbonate rocks composed largely of the minerals
calcite and dolomite. As part of a study of the stratigraphy of
Citrus and Levy counties (see Vernon, 1947, 1951) the Florida
Geological Survey sponsored a research project on the petrology
of the Eocene limestones which are there exposed. The aim of
this project was twofold, namely to provide data which might
supplement faunal studies in developing a detailed stratigraphic
zonation, and to clarify questions of rock origin, dealing with the
original deposition of the rocks and with the changes subsequently
wrought in them.
In order to gain regional perspective and to test the applica-
tion of petrographic methods to these rocks over considerable dis-
tances, the study was not restricted to the Citrus-Levy County area,
but was extended into Dixie County to the northwest, and into
Hernando and Pasco counties to the south (Fig. 1). The section
studied includes the upper portion of the Avon Park limestone, the
Inglis member of the Moodys Branch formation, and the Ocala
limestone (restricted) (Fig. 2), with which were included beds
now classified as the Williston member of the Moodys Branch for-
mation.
Location of Samples

Of the 299 samples studied, 32 subsurface cores are from Dixie
County, 87 cores and 118 surface samples from Levy County, and
62 cores from the Hernando-Pasco County area. The majority of
the subsurface samples are from core borings on file at the Florida
Geological Survey office. The locations of core holes are shown
in Table 1.

Acknowledgments
The work was carried out partly at the offices of the Florida
Geological Survey, partly at the Department of Geology, Columbia

University, and partly at the Department of Geology and Geog-
raphy of the University of Rochester. The samples from the Her-
nando-Pasco County area were made available by the Ohio Oil
Company.
The study was supervised by Professor Marshall Kay, to whom
the writer is deeply grateful for stimulation, help and advice. Spe-

cial thanks are due to Dr. Herman Gunter and Dr. Robert 0.
Vernon of the Florida Geological Survey for their help during the
study and in the preparation of the report; to Professor Paul Kerr
and his staff for aid in the mineral identification, and to Professor
Harold Alling for help in the analysis of thin-sections, in the in-
terpretation of data, and in the preparation of the manuscript.
Among the various geologists from whom the writer has received
aid are Dr. W. H. Twenhofel, Mr. and Mrs. Paul L. Applin, Mr.
David B. Ericson, Dr. C. Wythe Cooke, Mr. Joseph Banks, Dr.
Louise Jordan, Mr. H. Glen Walter, Dr. Hans Naegeli, and Mr. J.
Clarence Simpson (deceased March 29, 1952). To all of these he
expresses sincere thanks.

METHODS OF STUDY

Each sample was described under the binocular microscope and
analyzed for insoluble residues. In addition, some samples were
studied in thin-section.

Examination under Binocular Microscope

Examination at magnifications of 15 to 30 diameters served to
place the rock into one of the major categories of rock types rep-
resented-as being composed nf calcite, dolomite, or a mixture

45

v

FLORIDA GEOLOGICAL SURVEY

NW 5E
NW HMZNANDO-PAUco cCOuTINC
DIXIt COUNTY
< Lin /el one *

1---- W _ILL/STON MBR fl I

S... -MOODYS-BRA NCI- M-

AVON PARK LL ME TONE

Figure 2.-Eocene faces changes from Dixie County to Pasco County.

thereof, and as being laminated or massive. Notes were made on
color, texture, fossil content, and the presence of notable amounts
of non-carbonate material. Confirmatory tests for calcite and dolo-
mite were made with dilute hydrochloric acid, and in a few cases
with Lemberg's silver nitrate-potassium chromate staining method
(Krumbein and Pettijohn, 1930).

Insoluble Residues
From cores and hand-specimens, samples of 20 to 30 grams were
prepared for insoluble residue study. In the case of cores, a sepa-
rate sample was prepared for each lithologic unit, and in cases
of uniform lithology a sample was prepared for every five feet
wherever possible. An attempt was made to obtain a composite
sample of several chips from various parts of the interval sampled.
The sample was weighed to an accuracy of one gram, and was
then digested with dilute hydrochloric acid in a 600 or 1000 cc
beaker. After digestion the relative amount and color of the fine,
flocculant material slimess) was noted. Slimes and solution were
then decanted. The remaining coarse residue (silt and sand grades)
was repeatedly washed, and dried on a watchglass. The residue
was weighed to an accuracy of 0.01 gram, and the weight expressed
as percentage of the original rock sample. Volumetric methods
which have proved useful in insoluble residue studies elsewhere
which have proved useful in insoluble residue studies elsewhere

were not feasable, since despite the large samples used, the amount
of residue was commonly microscopic, and since in numerous sam-
ples the bulk of the residue consisted of lacy or spongy masses of
silica, which occupy a volumetric prominence far out of propor-
tion to their comparative weight.

The residue was studied under the binocular microscope, at
magnifications of 30 to 60 diameters. The various constituents
were identified and the quantity of each constituent in terms of
the entire residue was estimated by eye. In these estimates al-
lowance was made for differences in specific gravity, so that the
resulting figures could be converted into percent by weight of
the original rock sample. This method is admittedly crude, but
most of the constituents are present in such minute quantities
(0.001 to 0.1 per cent of the rock) that small errors in estimation
are not likely to change the overall aspect.

Finally the residues were filed in standard foraminiferal dry-
mount slides, and in special cases grains were mounted in Canada
balsam for study under the petrographic microscope.

47

FLORIDA GEOLOGICAL SURVEY

Thin-sections

Thin-sections were prepared by the writer for representative
rock-types. In order to facilitate pore-space studies, most of the
rock slices were impregnated, prior to sectioning, with bioplastic,
a synthetic polyester resin, stained with methylene orange. The
thin-sections were studied under the petrographic microscope, and
were quantitatively analyzed according to the Delesse-Rosiwal
method, by the use of a Wentworth stage.

Examination of the rocks under the binocular microscope, and
in thin-section under the petrographic microscope, yielded numer-
ous data on composition. The carbonate rocks studied are com-
plex in makeup, and are consequently subject to much variation.
However, three major classes may be recognized on the basis of
mineral composition: rocks composed mainly of (1) calcite (here
called limestone), (2) calcite and dolomite dolomiticc limestone),
and (3) dolomite (dolomite rock). The great bulk of rocks studied
are limestones (1), and dolomite rocks (3).
Within these major classes the chief variables seen under the
microscope are structure (presence or absence of lamination),
texture, porosity, color, fossil content, and the amount of carbona-
ceous matter and other "impurities."

TRUE LIMESTONES

Composition.

The limestones are largely composed of three calcareous con-
stituents, skeletal material, paste, and secondary calcite. These
occur in varying proportions.

Skeletal material. Most of the limestones studied are coquinas,
or "shell sands," in the sense that they appear to be composed
largely of skeletal material in the form of calcite shells, tests, and
ossicles, or fragments thereof. Actually there is also generally
considerable (but less apparent) paste and secondary calcite, which
fills the shells and cements the skeletal material. A few samples

REPORT OF INVESTIGATIONS NO. 9

contained less than five per cent skeletal matter, whereas most con-
tained between 40 and 70 per cent. It is the nature of these fossil
remains which determines the texture and to some extent the
porosity of the rock.
In most of the rocks studied, the greater part of the skeletal
matter (up to 56 per cent of total rock volume) is of foramini-
feral origin. Sma ll
Foraminifera, especial-
ly miliolids, are most
common (Figs. 3, 4, and
5), but in soine cases
I a r g e Foraminifera
(Amphistegina, valvuli- te brds r
nids, orbitoids, or cam-
erinid s) predominate 7m
(Fig. 7). In some beds

cially those of Peri-
archus, are quantita-
tively important. Skele-
tal elements of many
other groups of organ-
isms occur in minor Figure 4.-Thin-section of limestone. Large
quantities, generally not miliolid Foraminifera, an echinoid fragment
exceeding ten per cent with typical grid-structure, and other shell frag-
ments in matrix of medium to coarsely crystal-
of any one rock. Thus line calcite. Porosity shown in black. X 42. In-
remains of red algae glis member Moodys Branch formation (well
remains of red algae bottomed in Inglis), so far as samples show.
and green (for the most
part of the genus Dasycladus) algae are encountered (Fig. 5), bryo-
zoa are widely distributed, barnacle plates and the claws of the
ghost-shrimp Callianassa characterize certain beds, starfish ossicles
are locally common, and certain pelecypods and gastropods that had
shells of calcite rather than aragonite are minor rock-forming
constituents. In many cases the present composition of the rock
in terms of skeletal material is not a true reflection of the compo-
sition of the original sediment, as aragonitic skeletal matter, in-
cluding most of the pelecypod and gastropod shells as well as the
occasional remains of corals, has been removed by solution, leaving
only molds. If these be taken into account, the Mollusca in some
beds rivalled the Foraminifera as agents of sedimentation.
In most rocks the calcitic remains have undergone considerable

alteration, in some cases
so much as to render
them unidentifiable. The
degree of alteration de-
pends chiefly upon the
composition of the orig-
inal particles. Miliolids
and other small Fora-
minifera have lost the
chitinouss" organic
matter, and therewith
the coherence, of their
tests; the latter have
become chalky, and may
remain distinct from
the embedding matrix
or may blend with it
(Figs. 3, 5). Bryozoa
and large Foraminifera
appear to be more re-
sistant to alteration
(Fig. 7) but commonly
are also soft and chalky.
The calcitic remains of
mollusks, algae, and
echinoderms generally
show little alteration,
retaining their original
internal structure.

Past e. Extremely
fine-grained calcite,
termed calcite paste,
commonly makes up 20
to 50 per cent of the
rock, but is less con-
spicuous than the skele-
tal material. It is gen-
erally chalky (Fig. 3),
but in a few cases it
is firmly consolidated
(Fig. 5). While much

50

FLORIDA GEOLOGICAL SURVEY

Thin-sections

Thin-sections were prepared by the writer for representative
rock-types. In order to facilitate pore-space studies, most of the
rock slices were impregnated, prior to sectioning, with bioplastic,
a synthetic polyester resin, stained with methylene orange. The
thin-sections were studied under the petrographic microscope, and
were quantitatively analyzed according to the Delesse-Rosiwal
method, by the use of a Wentworth stage.

Examination of the rocks under the binocular microscope, and
in thin-section under the petrographic microscope, yielded numer-
ous data on composition. The carbonate rocks studied are com-
plex in makeup, and are consequently subject to much variation.
However, three major classes may be recognized on the basis of
mineral composition: rocks composed mainly of (1) calcite (here
called limestone), (2) calcite and dolomite dolomiticc limestone),
and (3) dolomite (dolomite rock). The great bulk of rocks studied
are limestones (1), and dolomite rocks (3).
Within these major classes the chief variables seen under the
microscope are structure (presence or absence of lamination),
texture, porosity, color, fossil content, and the amount of carbona-
ceous matter and other "impurities."

TRUE LIMESTONES

Composition.

The limestones are largely composed of three calcareous con-
stituents, skeletal material, paste, and secondary calcite. These
occur in varying proportions.

Skeletal material. Most of the limestones studied are coquinas,
or "shell sands," in the sense that they appear to be composed
largely of skeletal material in the form of calcite shells, tests, and
ossicles, or fragments thereof. Actually there is also generally
considerable (but less apparent) paste and secondary calcite, which
fills the shells and cements the skeletal material. A few samples

REPORT OF INVESTIGATIONS No. 9

Figure 7.-A. Thin section of foraminiferal (camerinid and orbitoid) lime-
stone, showing interstitial pore-space (black) and cementation of fossils by
secondary calcite (clear). x 42. From the Ocala limestone of western Dixie
County (subsurface).
B. Thin section of dolomite rock formed by replacement of foraminiferal
limestone. Note crudely preserved in lower center of field. Interstitial pore
space appears to have been maintained. x 13. From the Ocala limestone of
western Dixie County (subsurface).

of this material is of primary origin many thin-sections show a
gradation from recognizable, clearly bounded fossil shells through
shells with indistinct borders into paste with phantom fossils, in-
dicating that at least some of the paste is derived from the dia-
genetic break-down of skeletal material.

Secondary calcite. In rocks composed largely of skeletal matter,
with open spaces between the fossils, a thin crust of calcite crystals
commonly covers and cements the fossil particles (Figs. 3, 7). In
some cases cavities in the rock are partly or completely filled with
secondary calcite. Thus in the case of the limestone boulders of the
Moodys Branch formation found south of Gulf Hammock, the
molds left by aragonitic shells have been filled with coarsely crys-
talline calcite, producing casts of the originals.

In many cases the calcite paste grades into more coarsely
crystalline material which is evidently the result of recrystalliza-
tion, and in one bed (Fig. 4) the paste appears to have com-
pletely gone over into translucent, buff, coarsely crystalline calcite.

Many of the samples contain such small quantities of non-
carbonate matter that it is not apparent under the binocular micro-
scope and not identifiable in thin-section. Other samples are mottled
with smali quantities of pyrite, and many surface samples show
a limonite stain. Some of the rocks contain appreciable quantities
of carbonaceous matter (up to 12.4 per cent), and one of them
contains 3.7 per cent clay.

Porosity.
The two main types of visible pore-space are intersticial pores
between the constituent skeletal particles of coquina limestones,
and secondary cavities formed by the solution of aragonitic shell-
matter. In addition, there is intergranular pore-space, which is
too fine to be visible in thin-section. Visible porosity measured in
ten thin-sections ranges from 0 to 13 per cent, and values of 5 to 13
per cent aie representative of the rock-types most commonly en-
countered.

52

REPORT OF INVESTIGATIONS No. 9

Sedimentary structure.

With the exception of a single, finely laminated bed, the rocks
are characterized by a conspicuous lack of sedimentary structures.
There are few well-defined bedding planes, but a rude type of
massive stratification is produced by vertical changes in compo-
sition and cementation. The above mentioned exception is a bed
in the Avon Park limestone, exposed at the base of the Lebanon
quarry, and consists chiefly of calcite paste which is laminated with
thin layers of carbonaceous matter.

Color.
Most of the unweathered limestones are white to cream colored.
Some show a bluish-gray mottling due to pyrite. A few limestones
from the Avon Park are buff colored, probably because of finely
divided organic matter.

Changes on weathering.
Weathering generally causes "case hardening" of the rocks by
deposition of mineral matter at exposed surfaces. Some of the
limestones are partly replaced by silica, to form after continued
weathering and leaching a dull white, porous, friable mass of fine
grained quartz, containing crude molds and pseudomorphs of the
original calcite constituents. Weathering also commonly stains
the rock with limonite.

DOLOMITIC LIMESTONES

Limestone composed of a mixture of dolomite and calcite grains
are less common than nearly pure limestones or dolomite rocks, and
the examples found have come from zones of vertical or horizontal
transition from one rock type to the other. Thus, a fifteen-foot
sequence of cores from the Avon Park limestone of Dixie County
shows a white miliolid limestone at the base that is overlain by simi-
lar rock containing scattered buff dolomite rhombs in the chalky
paste between the miliolids. Above this a buff, finely crystalline, fri-
able dolomite rock which retains abundant white miliolids of chalky
calcite, grades upward into similar dolomite rock from which the
miliolid calcite has been removed, leaving a large amount of cellular
pore space.
Another dolomitic limestone shows the calcite paste and some

53

FLORIDA GEOLOGICAL SURVEY

of the chalky skeletal elements to be invaded and largely replaced
by dolomite rhombs (Fig. 6).

DOLOMITE ROCKS

Composition and texture.
The dolomite rocks consist chiefly of fine (about 0.01 mm.) to
medium grained (about 0.1 mm), buff colored, anhedral to rhombic
crystals of dolomite. In some rocks these crystals are interlocked
to produce a very hard
-. 'I sedimentary "marble."
'^." i In many of the finer
^i" grained rocks the crys-
r, :^ tals are merely in loose
:..... contact, and the rock is
4W. 1. friable.
,'t. J W A< 4'/' hir de i by the
...''. -' !In addition to tex-
Yt '.....:*: ture determined by the
L :s :.' size of the component
crystals, most of the
.i^'-r ^ dolomite rocks exhibit
',,..^ : texture which is inheri-
ted from the parent sed-
-iment. This inherited
texture may be posi-
Figure 9.-Thin section of dolomite rock tive or negative. The
derived from a limestone which contained abun-
dant camerinids. Pore-space shown in black, positive inherited tex-
Dolomitization has produced a rock of tightly ture is shown in Fig.
innerlocking, medium grained dolomite 'crystals
with irregular intercrystalline pore-spaces, and 7-B, a case in which
has obliterated the character of the parent sedi- skeletal constituents
ment except for the camerinids, which are pre-eta consuen
served as cavities (external molds). x8. From (larger Foraminifera)
the Ocala limestone of western Dixie County have been replaced by
(subsurface).
dolomite, and the inter-
stices have remained open. The negative inherited texture is more
common; in this, paste and pore-space of the original sediment have
become converted to dolomite, and former skeletal material is
represented by pore space (Figs. 8-9). In some cases dolomitization
leaves little or no pore space, and inherited texture in obscure,
represented by phantom outlines of skeletal elements which may
be observed only in thin-section.
Under the binocular microscope and in thin-section many of

REPORT OF INVESTIGATIONS No. 9 55

-'l -.--
Sire 1.-olised seio o a seien o lied oloie

rock. Note interbedding with thin beds of "massive" types, from
which burrows extend downward. X 1.6. From the Avon Park lime-
stone at the Lebanon Quarry, Levy County, see Vernon (1951, pp.
108-110) for section.

the dolomite rocks show little in the way of impurities except for
very finely divided material which clouds the sections and is com-
monly concentrated at crystal boundaries. Some rocks are speckled
gray or black with pyrite, and others are speckled gray with
minute quantities of "glauconite." These minerals are discussed
below, under the heading of insoluble residues. Carbonaceous mat-
.a -..L

ter is present in small quantities in virtually all of the dolomite
rocks and is sufficiently abundant in some to be apparent in hand-
specimens and thin-sections. It occurs in amorphorus form, or as
C /7-

porosity inherited from the parent limestone, as fossil mold porosity,
and as intercrystalline porosity (the latter commonly not visible in
thin-section). Fossil mold
porosity is even more
common in the dolomite
rocks than it is in the
limestones as not only
aragonitic skeletal re-
mains but also those
originally composed, of
calcite are most com-
Smonly represented as
i molds in the dolomite
rocks.

Sedimentary structure.
.* Like the limestones,
the dolomite rocks occur
Figure 11.-Thin section of laminated dolo- in two faces: the mas-
mite rock. Note fine texture with scattered
patches of medium-crystalline dolomite (cavity sive and the laminated.
killings) Organic laminae shown in black, The latter is not a rarity
pore-space by parallel lines, x 100. Sample e er a rari
from Avon Park limestone at the Lebanon like its calcareous equiva-
quarry, Levy County, for section see Vernon lent but occurs widely in
(1951, pp. 108-110).
the Avon Park limestone
(Figs. 10-11). The lamination is produced by the alternation of
thin beds of dolomite crystals and carbonaceous material. The car-
bonate layers are from 1 to 10 or more millimeters thick, largely
composed of finely crystalline dolomite (the crystals being generally
less than 0.01 mm. in diameter), but containing patches of some-
what coarser crystals. The carbonaceous material occurs as dis-
continuous laminae which may be as closely spaced as twelve in
one millimeter. Commonly these laminated beds of fine dolomite
are interstratified with thin beds of medium crystalline dolomite
(crystals generally ranging from 0.015 to 0.04 mm. in diameter).
These medium-grained beds are devoid of organic lamination, and
show much fossil porosity. They correspond to the usual massive
type of dolomite rock of the type illustrated in Figure 8.

Color.
The dolomite rocks studied are universally buff to brown. Some
show additional gray'mottling due to pyrite, "glauconite," or both,

56

REPORT OF INVESTIGATIONS NO. 9

and many are speckled or laminated with black carbonaceous
matter.

Compaction phenomena.
Whereas the limestones examined show no evidence of com-
paction after deposition, shells and echinoid tests in some (but not
all) of the dolomite rocks are flattened parallel to the bedding.
Thus abundant molds of Cassidulus (Fig. 12) occurring in a bed
of unconsolidated, fine grained dolomite rock (Vernon, 1951, pp.
129-30, bed 4) show compaction of up to 30 per cent. The molds
are marked by jagged fractures which follow the sutures of echi-
noid tests, indicating that the tests were collapsed as compaction
occurred. The tests subsequently were removed by solution.

Data Derived from Insoluble Residues
By dissolving and removing the carbonate portion of the rock,
constituents that make up only a fraction of a per cent of the rock,
and that are rarely seen in the rock itself, may be concentrated
and made available for study. These constituents may be separated
into three groups: (1) mineral grains derived from pre-existing
rocks, generally brought from afar, termed allogenic; (2) minerals
precipitated in place from solution, termed authigenic; and (3)
organic (carbonaceous) material.

ALLOGENIC MINERALS

Clastic quartz.
Quartz sand and silt comprise the greater part of most residues.

57

FLORIDA GEOLOGICAL SURVEY

Sand. Sand grains that lie free in the cavities of cores and
surface samples represent contamination of the Eocene limestones
from later Tertiary and Quaternary sources. Pleistocene sands
lie directly on the limestone over most of the area studied, and are
slowly being removed from the surface by sifting into solution
channels and other pore spaces of the underlying rock. In the pro-
cess of coring, some sand may have been pumped into the cores
with the drilling fluid, and some sand also may have been introduced
by later handling of the cores. No sand grains were seen to be
firmly embedded in the rocks, hence none are believed to be original
constituents of the sediments.

Silt. Some silt is probably derived from the same sources as
the sand, and represents contamination. Thin-sections and analyses
of tight, uncontaminated rocks indicate that there are also small
quantities (fractions of one per cent) of quartz silt which are
original constituents of the sediments.
Heary Minerals.
Ilmenite, zircon, garnet, and other "heavy minerals" accompany
the quartz sand and silt in variable proportions. As in the case
of the quartz, the majority of these grains represent contamination
from younger, overlying sediments, though it is likely that among
the silt-sized particles there are some which represent original con-
stituents of the Eocene rocks.

Clay Minerals.
All of the rocks studied contain insoluble matter in the size-
range of clay; some of this probably consists of true clay minerals.
In most cases this material comprises less than one per cent of the
rock, though the laminated limestone bed and the clayey limestone
bed of the Avon Park limestone in the Lebanon quarry (see Vernon,
1951, pp. 108-109) yielded 7.4 and 3.7 per cent of incombustible
clay-size material respectively. Occasional flakes of clay in the
coarse residues are due to contamination from Miocene and Plio-
cene (?) sediments that probably covered the entire area, and that
have been removed except for thin remnants.

AUTHIGENIC MINERALS

In addition to the authigenic grains of calcite and dolomite that
compose the bulk of the rocks studied, and that have been discussed
above, minor quantities of other authigenic minerals are found

58

REPORT OF INVESTIGATIONS NO. 9

in the insoluble residues. The authigenic minerals may be divided
into those formed before burial, called syngenetic, and those formed
after burial, called epigenetic. Both types are represented.

Pyrite.
Forty-nine per cent of the subsurface samples and three per
cent of the surface samples studied contained pyrite. This is
generally finely crystalline, and may occur either in scattered
crystals or in spongy aggregates of greenish gray or dull brassy
appearance. Small euhedra of pyrite are commonly seen in pellets
of "glauconite." While most of the pyrite aggregates are irregular,
some represent internal molds of Foraminifera, especially of milio-
lids. As little as 0.01 per cent pyrite may impart a gray mottling
to the rock. The discrepancy in the occurrence frequency of pyrite
in surface and subsurface samples (tables 2-3) is due to the
alteration of pyrite to limonite in the oxidizing environment at the
surface.

"Glauconite."
Among the most conspicuous elements of the coarse residues,
though rarely present in amounts exceeding a fraction of one per-
cent, is a soft, slightly translucent, clay-like substance. Many of the
grains are internal molds of foraminiferal tests (Fig. 13), and

59

FLORIDA GEOLOGICAL SURVEY

some have been observed in the interior of
echinoids (Peronella). The color varies from
sea-green and grass green to white and
brown; intermediate shades of olive green
and olive gray are most common. The oc-
currence of this mineral or group of min-
erals suggests glauconite, as does the green
Figure 13.-"Glau- color of some samples. The optical properties
conite," internal molds could not be studied in detail because of the
of foraminiferal cham-
bers, x 30. Moodys extremely small size of the crystal units
Branch formation, which compose the grains. Some of the grains
Dixie Couny.appeared optically isotropic (perhaps because
of crypto-crystalline structure) whereas others showed some bire-
fringence. The refractive indices of the grains diverged in some
cases widely from those reported for glauconite. The latter shows
a variation of na from 1.590 to 1.612, of nf from 1.609 to 1.643
and of ny from 1.610 to 1.644. The highest indices observed in
the insoluble residues were 1.590, and the pale grains showed in-
dices below that of balsam (1.537). Thus both true glauconite and
the "glauconite" of the residues studied show a wide range in re-
fractive index, but the range of the latter lies entirely below that
of the former. That this discrepancy may be partly due to changes
caused by the hydrochloric acid used in the preparation of the
residues is attested by the fact that "glauconite" grains which
were not treated with acid (seen in thin-sections of the rocks) all
showed indices higher than that of balsam (1.537).
Attempts to obtain an x-ray diffraction pattern failed, the pat-
tern showing only pyrite and quartz which were also present in
the sample. Not enough material could be obtained to run either
a thermal diffraction analysis or a chemical analysis. Although the
material has not been positively identified as glauconite, its af-
finities to that mineral have not been disproved. In general habit
it resembles glauconite more than any other mineral described, and
is therefore here referred to as "glauconite." Its occurrence fre-
quency is shown on tables 2 and 3.

Secondary Silica.
Secondary silica is widely distributed in the coarse residues, and
is occasionally seen in thin-sections. It takes the form of white
spongy, lacy masses (Fig. 14) consisting of variable proportions of
chalcedony and quartz. In some cases the quartz predominates and
forms more massive subhedral drusy aggregates while in other

60

REPORT OF INVESTIGATIONS No. 9

cases miliolids, echinoid fragments and other
rock constituents have been crudely replaced.
The distribution of authigenic silica does not
appear to be correlated with either strati-
graphic horizons or the occurrence of other
residues.
Limonite.
In the subsurface, limonite is absent, or Figure 14.-Authi-
genic silica, x 10. Avon
present in very small quantities. Most of the Park limestone, W-
samples that contained little or no carbona- 1197, 135.1-144.3 feet.
Marion County.
ceous matter yielded slimes colored various
shades of ochreous yellow and orange brown, by traces of limonite.
Many of the rocks on the surface are stained with larger quantities
of this material, derived from the weathering of pyrite or intro-
duced from overlying deposits.

CARBONACEOUS MATTER.

Some of the samples examined contain large quantities of car-
bonaceous matter, up to 12.4 per cent of the entire rock (laminated
limestone from the Lebanon Quarry). Insoluble residues show
the presence of small quantities of organic (carbonaceous) matter
in many rocks in which it is not apparent in hand specimen or thin-
section. Virtually all of the dolomite rocks and half of the lime-
stones studied contained some carbonaceous material, of which
the following types were recognized:

(1) Very finely divided matter, which slowly settles out of
suspension, has a greasy feel, and is highly adhesive. (2) Shreds or
irregular filamentous aggregates, visible at magnifications above
100 diameters. (3) Massive brown consolidated aggregates in
which no structure is visible. (4) Plant tissues in various stages
of preservation, some showing cellular structure: fragments of
leaves and stems of land plants and sea weeds. (5) Pollen grains
of various types. (6) Tiny, clear, spheroidal bodies that are in-
soluble in alcohol, ether, or butyl acetate, and take a deep brownish
red stain when treated with iodine in a medium of hydrochloric
acid. (7) Organic matter from the tests of invertebrate animals,
such as chitinous linings of foraminiferal tests (obtained in acetic
acid preparations from the laminated limestone of the Lebanon
quarry).

such as lamination and faunal composition appear to be more
nearly related to time lines. The distribution of allogenic minerals
could not be determined because of excessive contamination from
younger beds. Authigenic insoluble residues and organic matter
are more closely correlated with the type of carbonate (calcite or
dolomite) than with position in the stratigraphic column.

AVON PARK LIMESTONE

The upper portion of the Avon Park limestone is represented
by dolomite rock with some interbedded limestone in Dixie, Levy,
and Citrus counties, and by limestone in the Pasco-Hernando County
area. The rocks are partly massive, partly laminated. The lami-
natedi facies occurs near the top of the formation in Dixie, Levy and

REPORT OF INVESTIGATIONS No. 9

Citrus counties but has not been recognized in the Moodys Branch
formation or the Ocala limestone. The distribution of authigenic
constituents is shown in Table 4.

Organic matter is more widespread and occurs in greater quan-
tities in the Avon Park limestone than in either the Moodys Branch
formation or the Ocala limestone, and is present not only in dis-
seminated form, but also as fossil leaves and twigs. The massive
limestones of the Avon Park contain abundant miliolids, some
of which reach larger size than those of the overlying formations.
Among the larger Foraminifera, valvulinids are prominent.

INGLIS MEMBER OF MOODYS BRANCH FORMATION

In western Dixie County the Inglis member of the Moodys
Branch formation is entirely represented by gray, mottled ("glau-
conitic" and pyritic), slightly carbonaceous, hard dolomite rock.
In central and eastern Dixie County the upper portion is a massive
miliolid limestone. Over much of Levy County the lithology is
limestone, with traces of "glauconite," the lower portion contain-
ing abundant crab claws, mollusk molds and echinoids, whereas
the upper is a miliolid coquina. Along the Citrus-Levy County

border, the basal portion of the Inglis member grades into massive,
fine grained, poorly consolidated dolomite rock containing pyrite
and "glauconite." In the Hernando-Pasco County area the Inglis
member is present as a pure, fairly hard, mollusk-bearing miliolid
limestone. The only large Foraminifera which reach local promi-
nence as rock builders are comparatively small valvulinids.

OCALA LIMESTONE AND WILLISTON MEMBER OF MOODYS
BRANCH FORMATION

At the time the analyses were made the rocks now classified
as the Williston member of the Moodys Branch formation were
considered to be basal Ocala limestone by the writer. Samples from
these beds are therefore grouped with samples of the Ocala lime-
stone, which they resemble lithologically more than they resemble
the underlying Inglis member.
The Ocala limestone and Williston member of the Moodys
Branch formation are represented by true limestones in the entire
area except in western Dixie County. Here the Williston member
passes into carbonaceous beds of dolomite rock, and the Ocala
limestones are interbedded with similar rocks. The limestone are
massive, and tend to be more chalky than the limestones of the
Inglis member of the Moodys Branch formation. Many of them
are composed largely of altered small Foraminifera (including
miliolids) and shell fragments. Much of the Ocala limestone con-
tains abundant large Foraminifera (camerinids and orbitoids),
or mollusk remains. In the Pasco-Hernando County area the
Ocala limestone becomes slightly "glauconitic" and slightly car-
bonaceous. The distribution of authigenic residues is summarized
in Table 6.

INTERPRETATION
It was hoped that the data obtained would furnish new means
of correlation, and would shed new light on the origin of the rocks
and thereby on the conditions which existed in the region at the
time when the rocks were deposited.
Significance of data in correlation
No widespread zones of distinctive minerals were discovered.
Allogenic minerals could not be used because of excessive con-
tamination from younger beds. Organic matter, pyrite, and "glau-
conite" show great differences in vertical distribution in different
parts of the area (Figs. 2-15). In some cases the occurrence of these
constituents appears to be closely related to the occurrence of
dolomite, which was found to cut across the formation boundaries
established largely on faunal differences. Yet, the following gen-
eralizations can be made: (1) Throughout the area, the top of
the Avon Park formation is characterized by more carbonaceous
matter than is present in the overlying beds. (2) Over large parts
of Dixie County, the dolomite rocks of the Inglis member, Moodys
Branch formation are distinctively mottled gray by pyrite, and
may be differentiated on that basis from the overlying dolomite
rocks of the Ocala limestone. (3) In Levy and Dixie counties the
Ocala limestone is largely devoid of "glauconite," which is present
in the underlying rocks. This situation is reversed in the Hernando-
Pasco County area (Fig. 2). Zones established on the presence or
abundance of carbonaceous matter, pyrite, or glauconite may be
found useful for detailed subsurface work in limited areas, es-
pecially in thoroughly dolomitized sections. On a regional scale
correlation of these beds on the basis of mineral content does not
appear to be feasible.
ROCK ORIGIN
Limestones and dolomite rocks are each represented by a mas-
sive and by a laminated facies. Textures, fossils, and pore-space con-
figuration indicate that most of these rocks were derived from two
types of parent sediment: massive calcitic and aragonitic "shell
sands," and lime mud laminated with organic matter. Both of
these sediments find modern counterparts in the sediments being
deposited in the region of the Florida Keys.
Massive limestone.
The massive limestones are diagenetic alteration products of

65

FLORIDA GEOLOGICAL SURVEY

calcitic and aragonitic shell sands, containing variable amounts
of fine, chalky calcareous paste. Carbonaceous matter was present
in some cases, absent in others. The abundance of miliolids and of
large Foraminifera such as camerinids, orbitoids, and large valvuli-
ni(d, as well as the sporadic occurrence of calcareous algae indicate
deposition in warm waters, within the zone of light (maximum
depth 200 meters). Lack of stratification may be accounted for by
uniform sedimentation and by mixing of the sediment by burrowing
organisms; one of the latter, the ghost shrimp Callianassa, has
left abundant remains in part of the limestone of the Inglis member,
Moodys Branch formation. The abundant enthonic fauna and the
general scarcity of carbonaceous matter indicate deposition on well-
aerated bottoms.
The original sediment underwent considerable change. In
some cases "glauconite" formed in the empty chambers of foramini-
feral tests, while pyrite crystallized in or between the tests. The
aragonite, present mainly as the chief constituent of most mollus-
can shells, was in all cases removed in solution, leaving shell molds.
Calcite, on the other hand was precipitated from solution to form
secondary incrustations upon the original grains of the sediment,
thus cementing the loose sediment into rock. The less stable shells
disintegrated to chalk and in many cases blended with the paste.
In other cases the paste recrystallized, to grade into the secondary
calcite.

Laminated limestone.
The single example of the laminated limestone faces, from the
Avon Park limestone of the Lebanon Quarry (Vernon, 1951, p.
109, bed 2), is a virtually unaltered sediment of unconsolidated cal-
careous mud with laminations of carbonaceous matter. Small Fora-
minifera are present, but form only a small percentage of the
sediment. They are so well preserved that treatment with acetic
acid yields the chitinous chamber-linings of entire tests. The large
amount of organic matter, including what appear to be branches
of land plants, suggests deposition in shallow water, protected from
waves and currents. The writer has observed sediments of this
type around mangrove islands in Florida Bay.

Dolomite rocks.
The occurrence of the textural features of the limestones in
most of the dolomite rocks is strong indication that the latter are
largely a result of secondary dolomitization of limestone sediments.

66

REPORT OF INVESTIGATIONS NO. 9

In this process, rhombs of dolomite appear to form in the calcite
paste which lies between the shell fragments, foraminiferal tests
and other.skeletal constituents. Various stages of this process
are exhibited by samples of dolomitic limestones, ranging from
limestones with scattered dolomite rhombs in the paste to those in
which all of the paste has been dolomitized, and only the fossils
remain as calcite. Dolomitization may proceed beyond this, to
replace the fossils, and to fill the pore-space with dolomite crystals;
this results in a tight, hard rock of interlocking dolomite crystals,
of the type found in the deposits of the Moodys Branch formation
and the Ocala limestone of Dixie County. In most of the dolomite
rocks studied, dolomitization has gone only to partial completion,
and has been followed by solution of the remaining calcite, re-
sulting in a rock riddled by the molds of formerly calcareous fossils.
In some cases this removal of calcite has led to compaction of the
rock, as shown by up to 30 per cent flattening of enclosed fossils
(Fig. 12). Alteration of the rock may proceed by the deposition of
dolomite on the walls of cavities. The dolomite rhombs thus formed
tend to be larger and clearer than those which replace the paste.
They convert the fossil molds and other cavities into microscopic
geodes, and may fill them entirely.
All of the dolomite rocks studied may be explained in this
manner, as penecontemporaneous or epigenetic alteration products
of calcitic and aragonitic sediments. However, the question arises
as to whether some may not equally well be accounted for by
other processes. It is conceivable that some of the fine-grained,
friable dolomite rock showing little or no inherited texture was
formed as a primary chemical precipitate, or as a plastic sediment
derived from the physical breakdown of older dolomites possibly
exposed on nearby islands. If the sediment had accumulated as a
dolomite silt, either of chemical or plastic origin, then the rocks
might be expected to show some of the following features:
(1) Primary sedimentary structures such as bedding, ripple
marks, and cross-lamination.
(2) Valvulinid and other foraminiferal tests of dolomite. Ag-
glutinating organisms would have built their tests of dolomite,
picked up from the bottom.
Well defined bedding is shown only by the platy facies of these
rocks, laminated with organic matter. The absence of other sedi-
mentary structures suggests that these fine-grained friable dolomite
rocks are probably not of plastic origin. The fact that arenaceous

FLORIDA GEOLOGICAL SURVEY

Foraminifera such as the various valvulinids (Eodictyoconus,
Coskitolina, Dictyoconus, Discorinopsis and others) are found
preserved as molds only is taken as definite evidence that they built
their tests of calcite rather than dolomite, and that the bottom
sediment was chiefly composed of calcite.
Furthermore, it seems unwise, at the present state of our
knowledge, to postulate a large-scale precipitation of primary dolo-
mite on the sea floor, in the absence of evidence (1) from the mod-
ern ocean bottom (where such occurrences have not been observed),
(2) from the chemical laboratory (where dolomite has not yet
been formed under conditions approaching those of the ocean bot-
tom).
It therf.fore seems most reasonable to conclude that the dolomite
rocks studied are the result of secondary (possibly penecontemp-
oraneous) alteration of normal calcite and aragonite sediments,
the massive dolomites having been derived from the massive lime-
stones, the laminated dolomites from the laminated limestones.
The when, how, and why of dolomitization remain among the
most perplexing problems in sedimentation. A theoretical approach
to the problem will not yield conclusive evidence until the true
solubility constants of dolomite have been determined and until
chemists ire able to predict solubility relationships in such complex
solutions as sea water and connate waters. Thus the study of
(dolomitization is at present limited largely to an empirical approach.
The data furnished by microscopic study of the rocks and the in-
soluble residues were scanned for possible correlation of any fea-
tures with dolomitization, which might yield clues as to the en-
vironment in which dolomitization occurred. Such correlation was
found in the occurrence of carbonaceous matter. Out of a total of
70 subsurface samples of dolomite rock, 68 (97 per cent) yielded car-
bonaceous matter in the insoluble residues. Of the remaining two,
one contained pyrite (indicative of the presence of reducing sub-
stances, presumably organic matter, in the original sediment). The
distribution of these samples may be compared on Tables 2, 8, 4,
5, and 6. Only 88 per cent of the dolomite rock samples from sur-
face exposures yielded carbonaceous matter; this is believed to be
due to surface oxidation of organic matter, and to the difficulty of
recognizing small quantities of carbonaceous matter in slimes dis-
colored by limonite. Among limestones from the subsurface 62
per cent contained carbonaceous matter, among surface limestones
only 4 per cent (Tables 2 and 3).

68

REPORT OF INVESTIGATIONS No. 9

In summary, carbonaceous matter is present in virtually all
dolomite rocks but only in part of the limestones. This suggests that
the presence of carbonaceous matter may have been necessary for
dolomitization to take place. It seems likely that bacterial decompo-
sition products such as carbon dioxide, hydrogen sulfide, or am-
monia, may have played a decisive role in the chemical changes
within the original sediments, which led to the transmutation of
calcitic and aragonitic shell sands and muds into dolomite rock.

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REPORT OF INVESTIGATIONS No. 9

In summary, carbonaceous matter is present in virtually all
dolomite rocks but only in part of the limestones. This suggests that
the presence of carbonaceous matter may have been necessary for
dolomitization to take place. It seems likely that bacterial decompo-
sition products such as carbon dioxide, hydrogen sulfide, or am-
monia, may have played a decisive role in the chemical changes
within the original sediments, which led to the transmutation of
calcitic and aragonitic shell sands and muds into dolomite rock.